1. Field of the Invention
This invention relates to a communication device, and more particularly to a modem device for enabling a single communication line to be shared by a plurality of terminal, or external device, units.
2. Description of the Related Art
A modem, acronym derived from modulator-demodulator, is used to convert signals output from one type of equipment into a form suitable for input to another type. The modem is composed of a modulator for superimposing a data signal on a carrier wave according to a predetermined method, and a demodulator for receiving a modulated carrier wave and recreating the signal originally transmitted by removing the carrier wave.
Such a modem is usually connected between a respective terminal unit of a personal computer or the like and a communication line. Therefore, a plurality of modems corresponding to the number as of the terminal units are required when a plurality of terminal units are used in a single office or home, thereby increasing the installation cost.
A method for solving this problem is to share a single modem between a plurality of terminal units. In this method, the terminal units are connected to the single modem through a manual switch device, and the modem can be commonly accessed by switching the connection by manually operating the switch device.
However, in the above-mentioned conventional modem device, the switching operation between the terminal units was troublesome because it had to be manually carried out. If the terminal units are distantly spaced from each other, locating the switch device near any one terminal unit means that it becomes remote from the others, presenting a serious inconvenience to the users of the other terminal units when needing to carry out the switching operation. Although an alternative method by remotely controlling the switching operation is proposed, the main problem, that the switching must be manually operated, Is unchanged in any case.